1,612 research outputs found
Redistribution of phase fluctuations in a periodically driven cuprate superconductor
We study the thermally fluctuating state of a bi-layer cuprate superconductor
under the periodic action of a staggered field oscillating at optical
frequencies. This analysis distills essential elements of the recently
discovered phenomenon of light enhanced coherence in YBaCuO,
which was achieved by periodically driving infrared active apical oxygen
distortions. The effect of a staggered periodic perturbation is studied using a
Langevin and Fokker-Planck description of driven, coupled Josephson junctions,
which represent two neighboring pairs of layers and their two plasmons. In a
toy model including only two junctions, we demonstrate that the external
driving leads to a suppression of phase fluctuations of the low-energy plasmon,
an effect which is amplified via the resonance of the high energy plasmon. When
extending the modeling to the full layers, we find that this reduction becomes
far more pronounced, with a striking suppression of the low-energy
fluctuations, as visible in the power spectrum. We also find that this effect
acts onto the in-plane fluctuations, which are reduced on long length scales.
All these findings provide a physical framework to describe light control in
cuprates
Improved Torsion Pendulum for Ground Testing of LISA Displacement Sensors
We discuss a new torsion pendulum design for ground testing of prototype LISA
(Laser Interferometer Space Antenna) displacement sensors. This new design is
directly sensitive to net forces and therefore provides a more representative
test of the noisy forces and parasitic stiffnesses acting on the test mass as
compared to previous ground-based experiments. We also discuss a specific
application to the measurement of thermal gradient effects.Comment: 4 pages 1 figure, to appear in the Proceedings of the 10th Marcel
Grossmann Meeting on General Relativit
Torsion pendulum facility for direct force measurements of LISA GRS related disturbances
A four mass torsion pendulum facility for testing of the LISA GRS is under
development in Trento. With a LISA-like test mass suspended off-axis with
respect to the pendulum fiber, the facility allows for a direct measurement of
surface force disturbances arising in the GRS. We present here results with a
prototype pendulum integrated with very large-gap sensors, which allows an
estimate of the intrinsic pendulum noise floor in the absence of sensor related
force noise. The apparatus has shown a torque noise near to its mechanical
thermal noise limit, and would allow to place upper limits on GRS related
disturbances with a best sensitivity of 300 fN/Hz^(1/2) at 1mHz, a factor 50
from the LISA goal. Also, we discuss the characterization of the gravity
gradient noise, one environmental noise source that could limit the apparatus
performances, and report on the status of development of the facility.Comment: Submitted to Proceedings of the 6th International LISA Symposium, AIP
Conference Proceedings 200
Achieving geodetic motion for LISA test masses: ground testing result
The low-frequency resolution of space-based gravitational wave observatories
such as LISA (Laser Interferometry Space Antenna) hinges on the orbital purity
of a free-falling reference test mass inside a satellite shield. We present
here a torsion pendulum study of the forces that will disturb an orbiting test
mass inside a LISA capacitive position sensor. The pendulum, with a measured
torque noise floor below 10 fNm/sqrt{Hz} from 0.6 to 10 mHz, has allowed
placement of an upper limit on sensor force noise contributions, measurement of
the sensor electrostatic stiffness at the 5% level, and detection and
compensation of stray DC electrostatic biases at the mV level.Comment: 4 pages (revtex4) with 4 figure
Possibilities for Measurement and Compensation of Stray DC Electric Fields Acting on Drag-Free Test Masses
DC electric fields can combine with test mass charging and thermal dielectric
voltage noise to create significant force noise acting on the drag-free test
masses in the LISA (Laser Interferometer Space Antenna) gravitational wave
mission. This paper proposes a simple technique to measure and compensate
average stray DC potentials at the mV level, yielding substantial reduction in
this source of force noise. We discuss the attainable resolution for both
flight and ground based experiments.Comment: To be published in Advances in Space Research, COSPAR 2002 conference
proceedings (6 pages, 3 figures
Generalized observers and velocity measurements in General Relativity
To resolve some unphysical interpretations related to velocity measurements
by static observers, we discuss the use of generalized observer sets, give a
prescription for defining the speed of test particles relative to those
observers and show that, for any locally inertial frame, the speed of a freely
falling material particle is always less than the speed of light at the
Schwarzschild black hole surface.Comment: 20 pages, 1 figure, submitted to General Relativity and Gravitatio
Measuring the LISA test mass magnetic proprieties with a torsion pendulum
Achieving the low frequency LISA sensitivity requires that the test masses
acting as the interferometer end mirrors are free-falling with an unprecedented
small degree of deviation. Magnetic disturbances, originating in the
interaction of the test mass with the environmental magnetic field, can
significantly deteriorate the LISA performance and can be parameterized through
the test mass remnant dipole moment and the magnetic susceptibility
. While the LISA test flight precursor LTP will investigate these effects
during the preliminary phases of the mission, the very stringent requirements
on the test mass magnetic cleanliness make ground-based characterization of its
magnetic proprieties paramount. We propose a torsion pendulum technique to
accurately measure on ground the magnetic proprieties of the LISA/LTP test
masses.Comment: 6 pages, 3 figure
Kinematics and hydrodynamics of spinning particles
In the first part (Sections 1 and 2) of this paper --starting from the Pauli
current, in the ordinary tensorial language-- we obtain the decomposition of
the non-relativistic field velocity into two orthogonal parts: (i) the
"classical part, that is, the 3-velocity w = p/m OF the center-of-mass (CM),
and (ii) the so-called "quantum" part, that is, the 3-velocity V of the motion
IN the CM frame (namely, the internal "spin motion" or zitterbewegung). By
inserting such a complete, composite expression of the velocity into the
kinetic energy term of the non-relativistic classical (i.e., newtonian)
lagrangian, we straightforwardly get the appearance of the so-called "quantum
potential" associated, as it is known, with the Madelung fluid. This result
carries further evidence that the quantum behaviour of micro-systems can be
adirect consequence of the fundamental existence of spin. In the second part
(Sections 3 and 4), we fix our attention on the total 3-velocity v = w + V, it
being now necessary to pass to relativistic (classical) physics; and we show
that the proper time entering the definition of the four-velocity v^mu for
spinning particles has to be the proper time tau of the CM frame. Inserting the
correct Lorentz factor into the definition of v^mu leads to completely new
kinematical properties for v_mu v^mu. The important constraint p_mu v^mu = m,
identically true for scalar particles, but just assumed a priori in all
previous spinning particle theories, is herein derived in a self-consistent
way.Comment: LaTeX file; needs kapproc.st
Thermal gradient-induced forces on geodetic reference masses for LISA
The low frequency sensitivity of space-borne gravitational wave observatories
will depend critically on the geodetic purity of the trajectories of orbiting
test masses. Fluctuations in the temperature difference across the enclosure
surrounding the free-falling test mass can produce noisy forces through several
processes, including the radiometric effect, radiation pressure, and
outgassing. We present here a detailed experimental investigation of thermal
gradient-induced forces for the LISA gravitational wave mission and the LISA
Pathfinder, employing high resolution torsion pendulum measurements of the
torque on a LISA-like test mass suspended inside a prototype of the LISA
gravitational reference sensor that will surround the test mass in orbit. The
measurement campaign, accompanied by numerical simulations of the radiometric
and radiation pressure effects, allows a more accurate and representative
characterization of thermal-gradient forces in the specific geometry and
environment relevant to LISA free-fall. The pressure dependence of the measured
torques allows clear identification of the radiometric effect, in quantitative
agreement with the model developed. In the limit of zero gas pressure, the
measurements are most likely dominated by outgassing, but at a low level that
does not threaten the LISA sensitivity goals.Comment: 21 pages, 16 figures, submitted to Physical Review
Characterization of disturbance sources for LISA: torsion pendulum results
A torsion pendulum allows ground-based investigation of the purity of
free-fall for the LISA test masses inside their capacitive position sensor.
This paper presents recent improvements in our torsion pendulum facility that
have both increased the pendulum sensitivity and allowed detailed
characterization of several important sources of acceleration noise for the
LISA test masses. We discuss here an improved upper limit on random force noise
originating in the sensor. Additionally, we present new measurement techniques
and preliminary results for characterizing the forces caused by the sensor's
residual electrostatic fields, dielectric losses, residual spring-like
coupling, and temperature gradients.Comment: 11 pages, 8 figures, accepted for publication Classical and Quantum
Gravit
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